The present disclosure relates to active fault detection and isolation of dynamical systems, and more specifically, to plate-fin heat exchanger fouling identification.
An objective of an aircraft environmental control system (ECS) is to provide fresh air at appropriate conditions for the passengers and crew, while performing secondary heating and cooling to various aircraft components. ECSs are required to control the temperature of hot “bleed” air stream after compression. Cross-flow plate-fin heat exchangers are typically used in ECSs because of their small weight and volume relative to their heat transfer efficiency. FIG. 1 depicts a conventional (reference) aircraft ECS piping and instrumentation diagram. The ECS primary heat exchanger 2 uses ambient ram air 4 as the cold fluid side to decrease the temperature of the compressed bleed stream. As a result, aircraft operations expose the ECS, and in particular its cold side, to fouling from contaminants such as sand, dust, and salt.
Fouling in aircraft ECSs is most often caused by deposition of dust particles suspended in the inlet airflow. Particulate accumulation is a function of air flow rate, concentration of contaminants, and system temperature and pressure. The accumulation of contaminants on the ECS heat exchanger surface significantly reduces its heat transfer efficiency and performance over time while also increasing pressure drop, leading to significant costs from maintenance and component failures.